The present invention relates to frequency synthesizers.
Various frequency synthesizers have been proposed in the past. Frequency synthesizers of the type capable of providing highly stabilized operation as well as of permitting manual control to any desired frequency would require a number of quartz crystal elements, or involve the use of a variable ratio frequency scaler coupled to a single source of crystal-controlled oscillator. Another approach would be to employ a phase-locked loop. However, any one of these approaches provides frequency changes in only steps of discrete amount of frequencies. This is particularly disadvantageous for amateur radio transmitters where frequency must be continuously changed within a limited bandwidth for tuning purposes, as well as for record and tape playing apparatus where the rotation of their drive systems is controlled continuously with respect to a standard frequency.
Although it may be possible with the prior art approaches to meet such requirements by providing as many discrete steps as desired, a great number of circuit components will be necessary. Conventional LC or CR oscillators may serve the purpose of providing continuous frequency variations. However, frequency stability requirement cannot be satisfied.